Chronic blepharitis is one of the most common conditions seen in the ophthalmologist's office but is difficult to treat effectively. The disease is an extremely complex condition that manifests several different and overlapping arrays of signs and symptoms. It is often associated with keratoconjunctivitis sicca, bacterial infections, as well as sebaceous and meibomian gland dysfunction. This research project focuses on human subjects rather than animal models. Patients with all types of chronic blepharitis are being thoroughly evaluated from a clinical and laboratory standpoint. This is leading to the development of a classification system that is based not only on signs and symptoms but also on biochemical and microbial parameters. The basic premise underlying this research is that many of the signs and symptoms associated with chronic blepharitis are related to complex interactions between lipids, microflora, and other factors which ultimately result in abnormal meibum and subsequent lipid secretions. Thus, meibomian secretions are being evaluated biochemically to determine the composition of these secretions in normal individuals and in patients with chronic blepharitis. Because samples are small and the lipids are complex, gas chromatography - mass spectrometry is employed for analytical purposes. High pressure liquid chromatography is also used in order to achieve effective initial characterizations. In addition, isolated bacteria are being tested for production of specific exoenzymes such as lipases and esterases; other activity such as formation of cyclopropanes from unsaturated fatty acids is also being evaluated. Finally, secondary effects related to drugs and drug therapy are being evaluated since lipid analyses and microbial assays suggest that these may be quite important. Clinical trials will eventually be performed, based on these evaluations, thus permitting the ophthalmologist to select specific therapeutic treatments based on clinical signs and simple biochemical or microbial assays.